The present invention relates to a speed reducer for use in a yaw drive apparatus which rotates a wind power generation unit of a wind power generation apparatus in a substantially horizontal plane, and a yaw drive method and an apparatus for wind power generation apparatus using the speed reducer.
In general, the yaw drive apparatus of the wind power generation apparatus rotates a windmill power generation unit about a tower according to a wind in order that blades of the wind power generation apparatus can receive the wind, and rotates a ring gear provided at the tower.
The yaw drive apparatus is generally constructed by a general-purpose induction motor (the number of rotations is 1000 to 1800 rpm) and a plurality of reducing mechanism (the total reduction gear ratio is 1/1000 to 1/3000).
Most conventional speed reducers for use in the yaw drive apparatus of the windmill power generation apparatus use a speed reducer including five stage-planetary speed reduction mechanisms, for obtaining the high gear reduction ratio. The planetary speed reduction mechanism includes an input sun gear, a plurality of planetary gears engaged with the input sun gear at the periphery of the input sun gear, an internal gear member having internal teeth engaged with the plurality of the planetary gears at the periphery of the plurality of the planetary gears, and a carrier rotatably supporting the plurality of planetary gears. The total reduction gear ratio is about 77% (95%×95%×95%×95%×95% at each stage=about 77%).
The applicant of the present invention has proposed to construct the speed reducer as three stage speed reduction mechanism constituted by a first speed reducing portion, a second speed reducing portion connected to the first speed reducing portion, and an eccentric oscillating-type speed reduction mechanism connected to the second speed reducing portion (refer to JP-A-2003-83400).
Further, an example of the conventional yaw drive method and apparatus of the wind power generation apparatus having the construction to be described is disclosed in JP-A-2001-289149.
The above-described yaw drive apparatus including a first gear connected to the upper end of the tower, a second gear engaged with the first gear, a motor which is attached to the wind power generation unit capable of yawing, supported at the upper end of the tower and drivingly rotates the second gear for yawing the wind power generation unit, a hydraulic brake including an electromagnetic brake attached to the motor and using a friction plate, a brake disk fixed to the upper end of the tower, and a frictional-fixing type brake shoe which is provided to the wind power generation unit and interposes the brake disk in it using the hydraulic driving.
When the wind power generation unit is yawed by the motor, the electromagnetic brake and the hydraulic brake are turned into a non-braking state simultaneously with the start-up of the electrification to the motor, so that the motor and the wind power generation unit is released from the braking. On the other hand, when the yawing of the wind power generation unit is stopped, the electromagnetic brake and the hydraulic brake are turned into the braking state simultaneously with the stoppage of the electrification to the motor, so that the motor and the wind power generation unit are provided with the braking torque.
However, the maintenance of the former speed reducer including five stage-planetary speed reduction mechanisms was not good due to the long total length and the large capacity. Further, when the speed reducer is operated at a low temperature of −20° C. or less, the stirring resistance of a lubricant becomes large due to the five stage reduction, and a motor with a large output is needed for compensating the loss of the stirring resistance.
In the latter speed reducer including the three stage speed reducing portions, the optimum reduction gear ratio for obtaining high efficiency for yaw drive apparatus was not proposed.